Brief Description Of The prior Art
In Chem. Ber. 105, 3346-3356 (1972) Muller and Mertschenk disclose a method of preparing a transition metal complex with a seven-member ring ligand. Transition metals which have been utilized with such seven-membered cyclic ligands have included vanadium, chromium, iron, cobalt and titanium. These complexes each contain pi-bonded seven-membered ring ligands. This prior art literature disclosure specifically teaches the preparation of cycloheptatrienyl-(1,3-cycloheptadiene) chromium(-1). It does not disclose utilization of this compound in any type of polymerization procedure, or suggest that it exhibits any catalytic activity.
The polymerization of olefins using a chromium-containing catalyst system has been known for many years. Generally, the most effective of such chromium catalyst systems have employed calcined chromium on a silica-containing base. In all of such systems, so far as they are known, the chromium metal has been present in the catalyst complex in a positive valence form, and, most frequently, in the hexavalent form when such catalysts have been used for olefin polymerization.
In U.S. Pat. No. 4,105,844, olefins are polymerized with a catalyst which is formed by mixing a supported chromium oxide composite with an adjuvant which is 1,3,5-cycloheptatriene or an alkyl substituted derivative thereof. A silicon-containing material, such as silica, silica-alumina and the like, is the suggested base or support for the chromium oxide portion of this catalyst system. The catalyst contains from about 0.5 to about 4.0 weight percent of chromium, calculated as chromium oxide, based on the weight of the total support plus chromium oxide. The adjuvant can be added to the reactor as a separate stream in any solvent which is inert in the process. The adjuvant can also be used to pretreat the catalyst prior to charging it to the reactor.
The process described in U.S. Pat. No. 4,105,844 is directed to the production of normally solid ethylene homopolymers or ethylene copolymers, using the supported chromium complex and the adjuvant for the catalyst. The polymers are made by contact with the catalyst and adjuvant in either a particle-form process or in a solution-form process using the appropriate polymerization conditions. Such conditions are described in U.S. Pat. No. 3,939,137 for solution-form polymerization, and in U.S. Pat. No. 3,950,316 for particle-form polymerization.
U.S. Pat. No. 4,424,139 discloses methods for producing phosphate-containing chromium catalyst systems for olefin polymerization, and particularly phosphate-containing pibonded chromium catalyst systems for olefin polymerization. The particular chromium material here used is chromocene, in which the chromium is divalent. The divalent cation is coordinated by two relatively negatively charged cyclopentadienyl ligands. Among other supports indicated to be suitable for the chromium compound is aluminum phosphate. In one of the support structures, the aluminum and phosphorus components are selected so as to give an atom ratio of phosphorus to aluminum within the range of 0.2:1 to 1:1, preferably 0.6:1 to 0.9:1.
In the activation of the catalyst, temperatures in the broad range of from about 150.degree. C. to 1,000.degree. C. can be used with the time required for catalyst activation being from 1 minute to about 24 hours.